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HL: Halbleiterphysik
HL 30: Photovoltaik II
HL 30.3: Vortrag
Mittwoch, 10. März 2004, 15:45–16:00, H14
Quasi-Fermi-Level-Splitting in Cu(In1−xGax)Se2 from 300K-Photoluminescence — •Gottfried Heinrich Bauer1, Rudolf Brüggemann1, and Stephane Vignoli2 — 1Institute of Physics, Carl von Ossietzky University Oldenburg — 2Lab. PMCN (CNRS) University Claude Bernard Lyon1, France
The splitting of Quasi-Fermi levels in Cu(In1−xGax)Se2 prepared under pilot line production conditions with final cell efficiencies of 15 % has been studied with calibrated luminescence YPL at 300K and with AM1- equivalent photon fluxes. The PL data have been evaluated with respect to the chemical potential of the electron-hole ensemble/quasi-Fermi level splitting according to Planck’s generalized law for the emission of non-thermal equilibrium radiation from matter [1]. We have separated the Bose-Term of the luminescence by dividing the pl-yield by the absorptivity A(ω) derived from transmission/reflection. The spectral absorption of CIGS shows considerable subgap absorption in the entire regime of composition indicating a substantial density of states located in the gap, supported by recent photo capacitance experiments [2]. In comparison to the shift of the band gap with Ga concentration YPL shifts in energy only very weakly. Accordingly the energetic separation of the quasi-Fermi levels at 300K, determining maximum Voc, only marginally increases.
[1] P. Würfel, Physics of Solar Cells Physics, Wiley, 2003
[2] J.T.Heath, J.D. Cohen et al., Appl. Phys. Lett. 80, 4540 (2002).